Field of the Invention
The present invention relates to an image pickup element, a method for controlling an image pickup element, and an image pickup apparatus.
Description of the Related Art
There is known a phase difference detection method (deviation method) as a method for detecting a focus state of a photographing lens. In the phase difference detection method, a light flux that has passed through an exit pupil of the photographing lens is divided into two, and light fluxes divided into two are respectively received by a pair of sensors for focus detection. Then, based on light receiving amounts thereof, a deviation amount between a pair of image signals output from the pair of sensors for focus detection, namely, a relative positional displacement amount between a pair of images in a direction in which the light flux is divided is detected, to thereby directly obtain a drive amount of the photographing lens necessary to achieve an in-focus state. Therefore, a defocus amount and a direction thereof are obtained by conducting an accumulation operation one time with the sensors for focus detection, which enables a high-speed focus adjustment operation.
In Japanese Patent Application Laid-Open No. 2008-134389, there is disclosed a technology for realizing a high-speed phase difference AF while eliminating the need for a dedicated sensor for focus detection by providing an image pickup element with a phase difference detection function.
In Japanese Patent Application Laid-Open No. 2013-084742, a problem is focused on, where an area of a pixel is divided into a plurality of photoelectric converters to cause reduction in capacity that can accumulate photoelectric conversion signals per photoelectric converter, that is, to cause reduction in amount of photoelectric conversion charges that can be accumulated until saturation. After one of the divided photoelectric converters has been saturated, even when outputs of the photoelectric converters corresponding to the same microlens are added up, an output of the addition fails to exhibit a linear characteristic due to an influence of the saturation, and hence image quality deteriorates.
Therefore, in Japanese Patent Application Laid-Open No. 2013-084742, there is disclosed a technology for forming a pixel so that a signal charge of the photoelectric converter that has been saturated leaks into another photoelectric converter corresponding to the same microlens. With such a pixel structure, in Japanese Patent Application Laid-Open No. 2013-084742, linearity is improved, which is exhibited when the pixels corresponding to the same microlens are added up without losing a charge photoelectrically converted by the photoelectric converter that has been saturated.
However, according to the related art, a focus sometimes cannot be detected satisfactorily.